Applications such as video conferencing and multimedia streaming demand low-lag gigabit speeds. To support high speed wireless communication, 802.11 standards are being driven to improve channel bonding, an efficient method that increases data rate regardless of other technologies in use. However, inefficiency and unfairness issues arise when heterogeneous radios coexist in a contention domain. When a device operates in a wide channel that spans across multiple narrow channels, it has to defer its transmission to the time when all of the narrow channels are vacant. This is inefficient because the device cannot utilize the other narrow channels when only one narrow channel is occupied. Further, when there are narrow channel devices in more than one narrow channel, the devices that use channel bonding are harder to win media access opportunities because narrow channel devices may work independently in the non-overlapping narrow channels.
A natural solution is to revert to narrow channel operations. A recent work introduces a compound radio design that splits a wide channel into multiple narrow channels and uses them independently. The strategy is efficient when a device has small packets to multiple devices. However, when a device has a bulk of data to one receiver, it is more efficient to use multiple split narrow channels as one wide channel to increase spectral efficiency by removing the guard bands between contiguous narrow channels. Although this approach narrows the guard bands with sharp filters, signal spreading introduced by a sharp filter will increase the inter symbol interference (ISI). Addressing the ISI requires a tradeoff between spectral efficiency and capability of tolerating frequency offset.
The inefficiency and unfairness issues can be alleviated if a device does not need to wait for all narrow channels to be idle to initiate a transmission. Recent spectrum-agile designs have shown that it is practical to aggregate noncontiguous narrow channels as one channel. The flexibility of spectrum use is thus comparable to the approach noted above. However, current spectrum-agile designs are frame-based. Therefore, when a new channel becomes available, it cannot be utilized until the next frame. An unfairness issue arises as not all nodes get contention opportunities for the new channel. The new channel is invisible to nodes that are in transmission. Some nodes may never be able to acquire the channel.
Current spectrum-agile designs are also lack of an efficient mechanism to address the multiple access issue. When a narrow channel becomes available, several nodes may attempt to acquire it at the same time. Leaving contention resolution to the carrier sense multiple access with collision avoidance (CSMA/CA) may require a large contention window to reduce collisions. The high overhead is hard to cut because low collision probabilities are desired. A transmission may fail even when two nodes have a collision only in a small fraction of used spectrum.
After a transmitter has won some narrow channels, it needs to inform the receiver of the used spectrum; otherwise, the receiver is unable to decode packets sent by the transmitter. Using control packets to achieve spectrum agreement can introduce high overhead because of medium access contention and physical layer convergence procedure. A better spectrum agreement method is desired.
To address the inefficiency and unfairness issues in channel bonding, this disclosure introduces a dynamic channel bonding (DyB) protocol in which a node is allowed to initiate a transmission as long as there exist some idle narrow channels and the node gradually increases channel width during transmission when new narrow channels are sensed to be idle. The design imposes three challenges.
First, when some narrow channels become idle, the medium access contention is severe because a transmitter has to contend with nodes that are within the same band of spectrum and nodes whose spectrum is partially overlapped with its spectrum. Even if two nodes collide only in a small fraction of the used spectrum, their transmissions may fail. Therefore, it is critical to address the contention issue in wide band spectrum sharing, which is the key to ensure that nodes will benefit from channel bonding. In this paper, a compound preamble is designed to probe collisions in all channels at the same time and a parallel bitwise arbitration mechanism is introduced to resolve the collisions. Nodes are allowed to contend for different channels simultaneously with different priorities. A node is unlikely to lose all channels in a contention.
Second, dynamic channel bonding aggregates all narrow channels obtained by a transmitter as one wide channel. A challenge is the communication over uncertain channel combinations. If the receiver is unaware of the channels used by the transmitter, the receiver cannot decode any packet sent by the transmitter. To achieve spectrum agreement between transmitter and receiver, we design partial spectrum correlation that encodes the receiver's unique signature in the frequency domain in all channels used by the transmitter. The receiver calculates the expected results when its signature is present in each channel. Through correlating received signal with all expected results, the receiver is able to identify channels used by the transmitter. Although there are n expected results when the target wide band is divided into n narrow channels, the searching for the signature in all channels is parallelized.
Third, the transmitter was unable to monitor the media state while it is transmitting. Therefore, current designs are frame-based. Each frame will use the available spectrum fragments detected before transmission. This raises an unfairness issue for sharing channels. Because a node cannot contend for a channel that becomes available during transmission, the channel may be acquired by another node. It is possible that channels used by two nodes are never available to each other because their contentions are not synchronized. With advances in self-interference cancellation, it becomes feasible to detect new spectrum availability even during transmission without using another antenna. This allows dynamic channel bonding to break the frame-based structure, changing spectrum use during transmission.
This disclosure addresses the aforementioned challenges with a dynamic channel bonding method and integrates all components as a complete system. This section provides background information related to the present disclosure which is not necessarily prior art.